Heat accumulator for a vehicle

ABSTRACT

An accumulator (20) operating according to the layered storage principle is used in connection with the cooling loop of a vehicle, and includes charge alternation devices (34, 38) adapted to upper and lower storage regions (26, 28). The inflow and outflow velocity of the coolant should be between 0.1 and 0.5 m/s, and charging or discharging of the accumulator (20) should occur within 10 to 100 seconds. Inflow and outflow lines (32, 36) run within an insulation space (40) in the fashion of a thermosiphon.

FIELD OF THE INVENTION

The invention relates to insulated heat accumulators for use in theengine coolant loops of vehicles and that can be charged and dischargedrepeatedly by means of a heat transfer fluid flowing through at leastone inflow line and one outflow line that penetrate the insulation ofthe heat accumulator. The invention also concerns a method for chargingand discharging this type of heat accumulator.

BACKGROUND OF THE INVENTION

One example of a heat accumulator of the general type of concern isshown in DE 40 41 626. To avoid mixing of warm fluid with cold fluid inthe accumulator, this heat accumulator uses an intermediate accumulatorinto which cool fluid is introduced during discharge of the accumulator.The introduction of fluid into the intermediate accumulator forces warmfluid from the accumulator. The intermediate accumulator, for example,can be of a flexible bellows or piston-cylinder design. Such anaccumulator is a representative of the type often referred to as amembrane accumulator, and has recently been considered to an increasingextent for use in vehicles because it has the capability of supplyinglarge amounts of heat by avoiding mixing of cold fluid and warm fluid.

Another type of heat accumulator, which is also intended for use invehicles, is a latent heat accumulator, which includes an inner vessel,an accumulator core in which an accumulator medium, e.g., an accumulatorsalt, is situated, and an outer vessel with insulation provided betweenthe core and the outer vessel.

Advantageously, a latent heat accumulator has a large storage capacity.Offsetting this advantage, is a more limited discharge rate. Further,latent heat accumulators are quite costly to manufacture. They poseproblems in terms of disposal because of the polluting nature of thestorage medium. Membrane accumulators in this respect are preferred, butare still too expensive because of the membrane and the additionalrequired plumbing. Moreover, membrane accumulators do not have anacceptable useful life. Another significant drawback of both accumulatortypes is that their geometry is not easily modified to accommodateirregularly-shaped installation spaces within the engine compartment ofa vehicle. This is becoming increasingly important because the availablespace in vehicle engine compartments is diminishing as the number ofcomponents incorporated within engine compartments increases.

Another type of heat accumulator is a layered accumulator whichtypically is used in households and which exploits the higher density ofa fluid at cooler temperatures by introducing cool fluid into a lowerstorage space and withdrawing warm fluid from an upper storage space,with the least possible mixing of the cool and warm fluids. Layeredaccumulators typically have a storage volume of many cubic meters, whichis much larger than the previously discussed heat accumulators that areintended for use in vehicles. Further, layered accumulators are rarely,if ever, fully discharged. Accordingly, layered accumulators aretypically subject to different constraints than heat accumulatorsintended for use in vehicles.

SUMMARY OF THE INVENTION

It is the principal object of the invention to provide a new andimproved heat accumulator for use in the coolant loop of a vehicle, andmore specifically, to provide a heat accumulator for a vehicle that isoptimized in terms of heat storage capacity, with minimized mixing ofwarm coolant with cold coolant and minimized heat losses.

It is a further object of the invention to provide a heat accumulatorthat can be readily adapted to irregular installation spaces within theengine compartment of a vehicle.

It is yet another object of the invention to provide a heat accumulatorat a manufacturing cost that is reduced relative to conventional heataccumulators that are intended for use in vehicles.

These objects are achieved according to the invention in a heataccumulator surrounded by insulation and adapted for use in a coolingloop of a vehicle. The heat accumulator includes first and second flowlines penetrating the insulation for transferring coolant between theheat accumulator and the cooling loop. The heat accumulator furtherincludes structure for storing the coolant according to the layeredstorage principle. The structure includes an upper storage region spacedabove a lower storage region. A first charge alternation device isconnected to the first flow line and is located in the upper storageregion. The first charge alternation device has a shape adapted to thefirst storage region. The first charge alternation device defines afirst total flow area for transferring coolant between the first chargealternation device and the upper storage region. A second chargealternation device is connected to the second flow line and is locatedin the lower storage region. The second charge alternation device has ashape adapted to the lower storage region. The second charge alternationdevice defines a second total flow area for transferring coolant betweenthe second charge alternation device and the lower storage region. Thesecond total flow area is roughly the same order as the first total flowarea. The first and second flow lines extend over a vertical regionwithin the insulation to form a temperature barrier layer in the coolantbetween the heat accumulator and the cooling loop of the vehicle. Thisachieves a situation in which the temperature-barrier layer, produced bythe different densities of the cooling liquid at different temperatures,is established in the vertical regions of the first and second flowlines when there is no forced coolant flow, thereby largely preventingthe undesired discharge of the heat accumulator.

According to one facet of the invention, a method is provided forcharging and discharging a heat accumulator for a vehicle by thesimultaneous introduction and withdrawal of coolant to and from the heataccumulator. The method includes the steps of charging the heataccumulator by introducing warm coolant into the heat accumulator at acoolant flow velocity of about 0.1 to 0.5 m/s and a coolant flow ratesufficient to input at least 80% of the total amount of the heat of theaccumulator within 10 to 100 seconds, and discharging the heataccumulator by introducing cold coolant into the heat accumulator at acoolant flow velocity of about 0.1 to 0.5 m/s and a coolant flow ratesufficient to output at least 80% of the total amount of the heat of theaccumulator within 10 to 100 seconds.

Other objects and advantages will become apparent from the followingspecification taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a front elevation view of a heat accumulator with an irregularshape, illustrating one embodiment of the invention;

FIG. 2 is a right side elevation view of the heat accumulator of FIG. 1;

FIG. 3 is a front elevation view of a heat accumulator with the sameshape in the upper and lower storage space, illustrating a secondembodiment of the invention;

FIG. 4 is a right side elevation view of FIG. 3;

FIG. 5 is a front elevation view of a heat accumulator illustrating athird embodiment of the invention in which one flowline has an arcwithin the insulation and enters a lower storage space;

FIG. 6 is a right side elevation view of the heat accumulator of FIG. 5;

FIG. 7 is a view taken approximately along the line 7--7 in FIG. 1 of arotary outlet charge alternation device for use in the invention;

FIG. 8 is a section view taken approximately along the line 8--8 in FIG.7;

FIG. 9 is a front elevation view of an elongated charge alternationdevice having an intermediate level for use in the invention, with aportion of the device broken away;

FIG. 10 is a sectional view taken approximately along the line 10--10 inFIG. 9;

FIG. 11 is a front elevation view of another elongated chargealternation device for use in the invention;

FIG. 12 is a longitudinal sectional view taken approximately along theline 12--12 in FIG. 11;

FIG. 13 is a sectional view taken approximately along the line 13--13 inFIG. 11;

FIG. 14 is a sectional view of a double tube charge alternation devicefor use in the invention;

FIG. 15 is a sectional view taken approximately along the line 15--15 inFIG. 14; and

FIG. 16 is a discharge diagram illustrating the heat output and totalheat content vs. time of an accumulator made according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As seen in FIGS. 1 and 2, a heat accumulator 20 is provided with anirregular shape that is adapted to conform with an irregularinstallation space in an engine compartment of a vehicle. The heataccumulator 20 includes an inner housing 22, defining a storage volumeor space 24 divided into an upper storage region 26 and a lower storageregion 28. An outer housing 30 surrounds the inner housing 22 and afirst flow line 32 is connected to a first charge alternation device 34in the upper storage region 26. A second flow line 36 is connected to asecond charge alternation device 38 in the lower storage region 28. Theupper storage region 26 has an essentially rectangular cross-section andthe first charge alternation device 34 has an elongated shape adapted tothe shape of the upper storage region 26. The lower storage region 28has an essentially square shaped horizontal cross section, and thesecond charge alternation device 38 has a shape adapted to the shape ofthe lower storage region 28. Thus, each of the charge alternationdevices 34, 38 is shaped and sized to fit within its respective storageregion 26, 28. The heat accumulator 20 becomes significantly larger inboth length and width in the transition from the lower storage region 28to the upper storage region 26. The heat accumulator 20 is intended tobe installed in an automobile in the depicted position.

The heat accumulator 20 further includes insulation shown in the form ofa vacuum insulation space 40 that is defined by the outer housing 30 andthe inner housing 22. The vacuum insulation space 40 is filled with anappropriate insulation material that is introduced into the insulationspace 40 via a filling connector 42 in known fashion and sealed.

Respective connectors 44 are provided on the lines 32, 36 for connectionto the cooling loop 45 of a vehicle. Materials with good heat insulationproperties can be used in the region where the connectors 44 and lines32, 36 pass through the outer housing 30 to further reduce heat lossesoccurring by convection.

A pair of supports 46 are arranged between the inner and outer housings22, 30 and simultaneously serve as mounting points for the accumulator20.

After penetrating the insulation space 40 adjacent the lower storageregion 28, the lines 32, 36 run upward through a vertical region 50within the insulation space 40 and penetrate the inner housing 22 inorder to enter the upper storage region 26. The vertical region 50 is ofsufficient vertical height for the lines 32, 36 to act as thermosiphonswherein a temperature barrier layer is formed in the lines 32, 36 due tothe differing densities of the cool and warm coolant when there is noforced flow of the coolant. The temperature barrier layer largelyprevents undesired discharge of the heat accumulator 20.

For reasons of space, the line 36 penetrates the inner housing 22 justbeneath the line 32. This vertical spacing has no significant adverseeffect with respect to the insulation and the formation of a temperaturebarrier layer. The vertical spacing leads to manufacturing advantagesand allows a reduction in width of the upper storage region 26.

After entering the upper storage region 26, the line 32 extends directlyto the elongated charge alternation device 34, while the line 36 extendsin an arc within the storage space 24 downward to the charge alternationdevice 38.

FIGS. 3 and 4 show another embodiment of the heat accumulator 20 inwhich essentially identical elongated first and second chargealternation devices 34, 38 are provided in the upper and lower storageregions 26, 28 because the upper and lower storage regions 26, 28 haveessentially the same shape.

FIGS. 5 and 6 show another embodiment of the heat accumulator 20 that issimilar to the embodiment in FIGS. 3 and 4, but which utilizes analternative arrangement of the lines 32, 36. As best seen in FIG. 6,this embodiment has greater width than the embodiment of FIGS. 3 and 4.The greater width provides sufficient space for the line 36 to penetratethe insulation space 40 adjacent the lower storage region 28. The line36 extends upwardly within the insulation space 40 over the verticalregion 50 and includes an arc 52. The line 36 then extends downwardlywithin the insulation space 40 to enter the lower storage region 28 andconnect directly to the elongated charge alternation device 38. The line32 proceeds vertically upward within the insulation space 40 and entersthe upper storage region 26, in a manner similar to the embodiments ofFIGS. 1-4.

As seen in FIGS. 7 and 8, the charge alternation device 38 connected toline 36 of the embodiment shown in FIG. 1 is designed as a rotary outlet60 to which the line 36 is centrally connected. A plurality of vanes 62extend radially from the center 64 to the periphery 66 of the rotaryoutlet 60 and are provided with a corresponding setting angle 68 tocreate inflow/outflow openings 70. Because of this arrangement, coolantflowing into the lower storage region 28 experienceshorizontally-directed diversion and is initially distributed in thelower storage region 28, before rising upward with limited mixing withthe warmer coolant present in accumulator 20.

FIGS. 9 and 10 illustrate an elongated charge alternation device 34, 38suitable for use in the upper storage region 26 of the embodiment shownin FIGS. 1 and 2 and in the upper and lower storage regions 26, 28 ofthe embodiments shown in FIGS. 3-6. The elongated charge alternationdevice 34, 38 includes a horizontal intermediate wall 72 arrangedbetween longitudinal, vertical walls 74 to divide a space 76 into anupper space 78 and a lower space 80. The intermediate wall 72 runsroughly parallel to the bottom of the upper storage region 26 and has aplurality of inflow/outflow openings 82 sized to the flow rate of thecoolant so that the coolant is initially distributed in the upper space28 before it flows further through the inflow/outflow openings 82.Inflow/outflow of the coolant into the storage space 24 occurs throughinflow/outflow slits or openings 84, which are arranged on the longedges of the walls 74 adjacent the bottom of the walls 74.

FIGS. 11-13 illustrate another elongated charge alternation device 34,38 that is suitable for use in the upper storage region 26 of theembodiment shown in FIGS. 1 and 2 and in the upper and lower storageregions 26, 28 of the embodiments shown in FIGS. 3-6. In contrast to theembodiment shown in FIGS. 9 and 10, no intermediate wall, such as thewall 72, is provided in the elongated charge alternation device 34, 38shown in FIGS. 11-13. In this device 34, 38, the coolant is distributedin the space 76 and enters the storage space 24 through a series ofinflow/outflow openings 85 in the long side of the longitudinal walls 74adjacent to the bottom of the walls 74. Tabs 86 at one side of theopenings 85 are bent inward and improve turbulence and distribution overthe entire length of the charge alteration device 34, 38.

In both of the embodiments shown in FIGS. 7-11, the space 76 is boundedon the top by a closure 88 shaped like a peaked roof. The longitudinaledges of the roof closure 88 extend laterally roughly above the verticallongitudinal walls 74. This has flow advantages because the coolantflowing down at this site experiences diversion.

The components of the device 34, 38 shown in FIGS. 7-11 can be producedas extruded sections.

FIGS. 14 and 15 illustrate yet another elongated charge alternationdevice 34, 38 that is suitable for use in the upper storage region 26 ofthe embodiment of FIGS. 1 and 2 and in the upper and lower storageregions 26, 28 of the embodiment shown in FIGS. 3-6. The elongatedcharge alternation device 34, 38 has a double tube construction andincludes an inside tube 90 having many relatively small inflow/outflowopenings 92 sized so that the coolant is first distributed throughoutthe interior of the tube 90 before it reaches an outside tube 94. Theoutside tube 94 has larger inflow/outflow openings 96 which are situatedon the opposite side of the device 34, 38 from the openings 92, therebycausing the coolant to travel a longer distance within the tube 94 andto enter the storage space 24 uniformly through all of the openings 96.

It should be appreciated that the flow of coolant into the storage space24 is indirect with limited mixing of the cool and warm coolant for allof the embodiments of the charge alternation device 34, 38 shown inFIGS. 7-15. The degree of mixing depends on the inflow velocity of thecoolant. The inflow velocity is therefore preferably between about 0.1and 0.5 m/s. Extensive experiments have shown that this velocity rangeachieves the necessary frequent charge alternation with a satisfactorilylimited degree of mixing.

Preferably, for any given accumulator 20, the sum of the areas of theinflow/outflow openings 70, 84, 85, 96, (i.e., the sum of the flow crosssections) in one of the charge alternation devices 34, 38 is of roughlythe same order as the sum of the areas of the inflow/outflow openings70, 84, 85, 96 in the other charge alternation device 34, 38 in theaccumulator 20. These areas are calculated and laid out so that thecoolant arriving via the lines 32, 36 is reduced in flow rate so that onentering the heat accumulator 20 the coolant exhibits the desired flowvelocity of between 0.1 to 0.5 m/s. When the described chargealternation devices 34, 38 are used at this flow velocity, surprisinglygood introduction of the coolant without mixing is possible and goodresults overall can be achieved for the proposed application.

In operation the accumulator 20 can be charged and dischargedalternately with reversal of the flow direction into and out of theaccumulator 20. This procedure is adequate for smaller storage volumes(roughly between 4 and 10 liters) and will primarily be used inpassenger cars, since they undergo numerous starts and are frequentlyused for short trips. This procedure is optimized in terms of dischargeand charging. During discharge, the cold coolant flows into the lowerstorage region 28 and the heat of the accumulator 20 is almostcompletely discharged and made ready for use in the shortest time(within 10 seconds) with the use of state of the art coolant pumps,which have a coolant flow rate of about 1200 L/min. Almost completecharging or discharging of the accumulator 20 means that at least 80% ofthe total amount of heat within the accumulator 20 is delivered within10-100 seconds. The total amount of heat within the accumulator 20includes heat stored in the material of the accumulator that cannot beutilized. Thus, almost all of the effectively usable heat in the coolantis discharged during the delivery period. During charging, the flowdirection of the coolant is reversed, with the warm coolant flowing intothe upper storage region 26 so that small amounts of heat can be rapidlysupplied to the accumulator 20 while maintaining the temperaturelayering in the accumulator 20. Known control and regulation equipmentare present in the coolant loop for reversing the flow direction. Inthis manner, about 80% of the total amount of heat within theaccumulator 20 can be exchanged about 300 times per hour for a smallstorage space 24 of about 4 liters with a coolant flow rate of about1200 L/H and about 60 times per hour for a large storage space 24 ofabout 10 liters with a coolant flow rate of about 600 liters per hours.In other words, a period of about 10 to 60 seconds is available forcharging or discharging of the accumulator 20.

Alternatively, charging and discharging can occur without reversal ofthe coolant flow direction. Charging and discharging occur in thisprocedure by introducing the coolant into the lower storage region 28.This procedure is only optimized with respect to discharging. Optimizeddischarge is particularly important in heat accumulators of vehiclesbecause supplying a large amount of stored heat as quickly as possibleis desirable during a cold start to reduce exhaust emissions, passengercompartment heating, etc. In addition, this procedure utilizes lesscostly control technology. This procedure will be more suitable forsomewhat larger storage spaces 24 of about 7 to 15 L, which provide alarge amount of available stored heat and, therefore do not requirerapid charging.

FIG. 16 shows a discharge diagram in which the heat output from anaccumulator 20 and the total amount of heat within the accumulator 20according to the invention are plotted versus time. The heat outputremains roughly constant over a period of about 40 seconds, because thelimited mixing between the warm and cold coolant during this period hasno effect on the temperature of the outflowing liquid. This is shown bycurve 1. Curve 2 illustrates that about 80% of the total amount of heatis released during the same time. Curve 2 then changes to a much morelimited slope which shows that mixing of the warm and cold coolant isoccurring.

It should be appreciated that the special configurations of the chargealternation devices 34, 38 permit introduction of the coolantessentially without mixing. It should be particularly appreciated thatthe charge alternation devices 34, 38 can be adapted to theconfiguration of the heat accumulator by using charge alternationdevices 34, 38 of different design, such as the rotary outlet 60 shownin FIGS. 7, 8 and the elongated devices 34, 38 shown in FIGS. 9-15. Witha longer and relatively flatter shaped heat accumulator 1, an elongateddevice 34, 36 such as those shown in FIGS. 9-15 is used. With an uprightcylindrical shape or a roughly square cross section, a rotary outlet 60is used as a charge alternation device 34, 38. For example, a rotaryoutlet 60 may exhibit the most favorable results in an upper storageregion 26, whereas an elongated device proves to be the best chargealternation device 34, 38 in a lower storage region 28 (or vice-versa).Heat accumulators 20 with irregular shapes are thus made available to bemounted in cramped, irregular installation spaces within an enginecompartment.

It must be viewed as quite surprising that a layered accumulator is bestsuited in an automobile, where there are very frequent starts and shorttrips that are accompanied by continuous charging and discharging of theaccumulator.

The complete absence of conventional accumulator components, such as anintermediate accumulator or an accumulator core with a latent storagemedium, entails distinct advantage with respect to manufacturing costs.Further, the inadequate useful life associated with conventional heataccumulators is also extended for the same reasons.

What is claimed is:
 1. In a heat accumulator surrounded by insulationand adapted for use in a cooling loop of a vehicle, the heat accumulatorincluding first and second flow lines penetrating the insulation fortransferring coolant between the heat accumulator and a cooling loop ofa vehicle, the improvement wherein the heat accumulator furthercomprises:means for storing a coolant according to a layered storageprinciple, said storing means including an upper storage region spacedabove a lower storage region; a first charge alternation deviceconnected to the first flow line and located in the upper storageregion, the first charge alternation device having a shape adapted tothe upper storage region, the first charge alternation device defining afirst total flow area for transferring coolant between the first chargealternation device and the storing means; a second charge alternationdevice connected to the second flow line and located in the lowerstorage region, the second charge alternation device having a shapeadapted to the lower storage region, the second charge alternationdevice defining a second total flow area for transferring coolantbetween the second charge alternation device and the storing means, thesecond total flow area being roughly the same order as the first totalflow area; and wherein each of the first and second flow lines extendover a vertical region within the insulation to form a temperaturebarrier layer in the coolant between the storing means and a coolingloop of a vehicle.
 2. The improvement of claim 1 wherein the first andsecond flow lines penetrate the insulation adjacent the lower storageregion, extend roughly vertically within the insulation over thevertical region, and enter the upper storage region vertically spacedfrom each other, the second flow line extending downward within thestoring means from the upper storage region to the lower storage regionto connect with the second charge alternation device.
 3. The improvementof claim 1 wherein the second flow line penetrates the insulationadjacent the lower storage region, extends upward within the insulationover the vertical region to an arc section, extends downward from thearc section to a location adjacent the lower storage region, enters thelower storage region, and leads directly to the second chargealternation device.
 4. The improvement of claim 1 wherein the first andsecond flow lines penetrate the insulation above the lower storageregion, extend downward within the insulation to respective arcsections, extend upward within the insulation over the vertical regionfrom the arc sections to adjacent the upper storage region, and enterthe upper storage region, the second flow line extending downward withinthe storing means from the upper storage region to the lower storageregion to connect with the second charge alternation device.
 5. Theimprovement of claim 1 in combination with a cooling loop of a vehiclethat can only supply coolant flow to the second flow line and receivecoolant flow from the first flow line; and wherein the storing means hasa volume of about 4 to 15 liters.
 6. The improvement of claim 1 whereinthe first and second charge alternation devices are substantiallyidentical in shape.
 7. The improvement of claim 1 wherein the upperstorage region is shaped differently than the lower storage region. 8.The improvement of claim 1 wherein at least one of the first and secondcharge alternation devices is a rotary outlet with essentially equallength and width dimensions.
 9. The improvement of claim 8 wherein therotary outlet is circular and includes vanes extending in radial fashionfrom a center location to a periphery of the rotary outlet, each of thevanes set at an acute angle relative to vertical.
 10. The improvement ofclaim 1 wherein at least one of the charge alternation devices hasgreater length than width and includes at least one row of flow openingsfor transferring flow between the at least one of the charge alternationdevices and the storing means.
 11. The improvement of claim 10 whereinthe at least one of the charge alternation devices further comprises aouter tube, an inner tube located coaxially within the outer tube, afirst row of flow openings through the inner tube, and a second row offlow openings through the outer tube.
 12. The improvement of claim 10wherein the at least one charge alternation device further comprises:alongitudinally extending, upper closure in a shape of a peaked roof; andtwo laterally spaced, longitudinally extending, vertical walls connectedby the upper closure to define a charge space between the walls and theupper closure, each of the walls having a long side adjacent to asurface of the storing means.
 13. The improvement of claim 12 whereineach of the walls includes a series of flow openings on its long side,the flow openings defined by inwardly bent cutouts.
 14. The improvementof claim 12 wherein the at least one of the charge alternation devicesfurther comprises a longitudinally extending, horizontal wall thatdivides the charge space, the horizontal wall including a plurality offlow openings; and wherein each of the vertical walls includes a flowopening in the form of a slit on its long side.